The present invention relates to a photothermographic recording material and in more detail to a photothermographic recording material which exhibits improved distinguishability between the front and the back surface.
Heretofore, in the graphic arts and medical fields, effluent resulting from wet processing for image forming materials has caused problems with workability. In recent years, from the viewpoint of environmental protection as well as space saving, a decrease in said processing effluent has been increasingly demanded. As a result, techniques have been needed, which relate to photothermographic materials which can be efficiently exposed employing laser image setters and laser imagers, and can form clear black-and-white images exhibiting high resolution.
Said techniques are described in, for example, U.S. Pat. Nos. 3,152,904 and 3,487,075, as well as Morgan et al., xe2x80x9cDry Silver Photographic Materialsxe2x80x9d in Handbook of Imaging Materials, published by Marcel Dekker Inc., page 48, 1991. Further, photothermographic recording materials (hereinafter simply referred to as recording materials) are known, which comprise a support having thereon organic silver salts, light-sensitive silver halide grains, reducing agents, and binders.
Said photothermographic recording materials form photographic images utilizing heat development and comprise reducible silver sources (being organic silver salts), light-sensitive silver halides, reducing agents, and if desired, image color control agents which control the color of silver images, which are commonly dispersed into an (organic) binder matrix. Said photothermographic recording materials are stable at room temperature. However, when, after image exposure, they are heated to a relatively high temperature (for example, 80 to 140xc2x0 C.), images are formed by development. When heated, silver is formed through an oxidation-reduction reaction between said organic silver salts (which work as oxidizing agents) and said reducing agents. The rate of said oxidation-reduction reaction is enhanced by the catalytic action of a latent image which has been formed by exposed silver halides. Silver, which is formed through the reaction of organic silver salts in the exposed area, provides a blackened image portion, while the unexposed area remains as it is, whereby an image is formed. Said reaction proceeds without supply of any processing solutions such as water.
When these photothermographic recording materials are employed as graphic arts materials, after heat development, a press plate is commonly exposed through the resultant material and is employed for printing. When said exposure to the press plate is carried out, the front and the back of said photothermographic material are distinguished. However, when distinguishability between the front and the back surface is difficult, namely the front and the back surface exhibiting no visual difference, sufficient care is required for ascertaining that. As a result, a decease in work efficiency results.
From the viewpoint of the foregoing, the present invention was achieved. It is an object of the present invention to provide a photothermographic recording material which exhibits excellent distinguishability between the front and the back surface and increases efficiency of press-plate making work.
The object of the present invention has been achieved employing the following embodiments.
(1) A photothermographic recording material comprising on one side of a support an image recording layer comprising a light-insensitive organic silver salt, a photosensitive silver halide, a reducing agent for silver ions and a binder, wherein the difference in specular glossiness at an angle of 60xc2x0 between a thermally developed exposed area of the image recording layer and the bottom support surface opposite the thermally developed exposed area is at least 15.
(2) The photothermographic recording material of item (1), wherein the specular glossiness of the thermally developed exposed area of the image recording layer is smaller than the specular glossiness of the bottom support surface opposite the thermally developed exposed area.
(3) The photothermographic recording material of item (1), wherein the image recording layer further comprises a high contrast agent represented by Formula (1), 
wherein each R1 and R2 is independently a substituent group and at least one of R1 and R2 represents a cyano group; and M represents H or an alkali metal atom.
(4) The photothermographic recording material of item (1), wherein the image recording layer further comprises a high contrast agent represented by Formula (2), 
wherein L1 represents a divalent organic group which is capable of forming a ring; and M represents H or an alkali metal atom.
(5) The photothermographic recording material of item (1), wherein the recording material further comprises an adjacent layer in direct contact with the image recording layer, and at least one of the image recording layer and the adjacent layer comprises a high contrast agent represented by Formula (1), 
wherein each R1 and R2 is independently a substituent group and at least one of R1 and R2 represents a cyano group; and M represents H or an alkali metal atom.
(6) The photothermographic recording material of item (1), wherein the recording material further comprises an adjacent layer in direct contact with the image recording layer, and at least one of the image recording layer and the second layer comprises a high contrast agent represented by Formula (2), 
wherein L1 represents a divalent organic group which is capable of forming a ring; and M represents H or an alkali metal atom.
The present invention will now be detailed.
The invention according to item (1) is characterized in that specular glossiness difference (in terms of an absolute value) between the surface of a blackened area after development on the side which is coated with an image recording layer and the surface on the side which is not coated with said image recording layer is at least 15 at a measured angle of 60 degrees. Further, the invention according to item (2) is characterized in that glossiness difference between the surface of a blackened area after development on the side (hereinafter occasionally referred to as an image recording layer side), which is coated with an image recording layer, and the surface on the side, which is not coated with said image recording layer, is at least 15 at a measured angle of 60 degrees, and in addition, glossiness of the surface on the side (hereinafter occasionally referred to as a backing layer side) which is not coated with said image recording layer is greater than that of the surface on the side coated with said image recording layer.
The specular glossiness at a measured angle of 60 degrees, as described in the present invention, refers to the value determined in accordance with JIS Z8741, and is expressed by glossiness with respect to a glass surface at an incident angle of 60 degrees. ISO 2813:1994 is a International Standard which corresponds to JIS Z8741. The title of ISO 2813 is xe2x80x9cPaints and varnishesxe2x88x92Determination of specular gloss of non-metallic paint films at 20xc2x0, 60xc2x0 and 85xc2x0xe2x80x9d. Even though the glossiness of the image recording layer side in the present invention is not definitely determined due to the fact that relative glossiness with the backing layer side is taken into account, said glossiness is preferably from 40 to 70, is more preferably from 45 to 65, and is most preferably from 50 to 60. Further, even though glossiness of the backing layer side is also not definitely determined due to the fact that the relative glossiness with the image recording layer side is taken into account, said glossiness is preferably from 55 to 100, is more preferably from 70 to 95, and is most preferably from 80 to 95. It is characterized that the absolute value of glossiness difference between the image recording layer side and the backing layer side is at least 15. Further, said difference is preferably from 15 to 50, is more preferably from 20 to 45, and is most preferably from 25 to 45.
The glossiness in accordance with the present invention can be determined, employing for example, a glossmeter GM-268, manufactured by Minolta Co., Ltd., a digital variable angle glossmeter Type UGV-5D, manufactured by Suga Shikenki Co., Ltd., or a digital variable angle glossmeter Type VG-1D, manufactured by Nihon Denshoku Kogyo Co., Ltd.
In order to adjust the front and the back of recording materials to the desired glossiness, there are a method in which fine particles are incorporated into a layer, and a method in which minute phase separation is generated by employing a plurality of polymers as binders. However, theses methods are not particularly limited. One of the simplest methods in the present invention is that by suitably selecting the shape, particle diameter, or added amount of matting agents which, are added to the image recording layer side as well as the backing layer side, it is possible to obtain the desired glossiness of each layer side.
Another method, which controls the glossiness of both sides of said recording material, includes one in which minute phase separation is performed by employing a plurality of polymers as binders. In said method, a plurality of resins is blended with resins which constitute the uppermost layer, and the resultant glossiness is adjusted utilizing phase separation. The type of blending resins used is not particularly limited. However, depending on said blended resins, the following cases may occur. Said phase separation is not noted at all whereby no effects on glossiness are exhibited. Said phase separation occurs excessively, whereby haze and/or coatability degradation occur.
Listed as one example of the preferred combination of a plurality of resins to control glossiness is a combination of cellulose acetate butyrate and cellulose acetate propionate. Compared to the case in which both resins are employed individually, when both resins are blended, the resultant glossiness is lowered to result in an effective measure to distinguish between the front and the back surface. The blending ratio of both resins is preferably from 10:90 to 90:10, and is more preferably from 20:80 to 80:20.
Matting agents usable in the present invention will now be detailed.
The materials of matting agents usable in the present invention may be either organic or inorganic. Employed as inorganic materials may be, for example, silica described in Swiss Patent No. 330,158, glass powder described in French Patent No. 1,296,995, and carbonates of alkali earth metal or cadmium and zinc described in British Patent No. 1,173,181. Employed as organic matting agents are starch described in U.S. Pat. No. 2,322,037; starch derivatives described in Belgian Patent No. 625,451 and British Patent No. 981,198; polyvinyl alcohol described in Japanese Patent Publication No. 44-3643; polystyrene or polymethacrylate described in Swiss Patent No. 330,158; polyacrylonitrile described in U.S. Pat. No. 3,022,169; and polycarbonate described in U.S. Pat. No. 3,022,169.
The form of matting agents may be either regular or irregular, but a regular form is preferred, and a spherical shape is preferably employed. The particle size of said matting agents is expressed by the diameter of a sphere which has the same volume as the particle. The particle diameter of said matting agents, as described in the present invention, is to be the diameter of a sphere which has the same volume as that of said particle.
The average particle diameter of the matting agents, employed in the present invention, is preferably from 0.5 to 20 xcexcm, and is more preferably from 1.0 to 15.0 xcexcm. Further, the variation coefficient of the particle size distribution is preferably 50 percent or less, is more preferably 40 percent or less, and is most preferably 30 percent or less.
Herein, the variation coefficient of the particle size distribution is the value represented by the formula given below:
{(standard deviation of particle diameter)/(average of particle diameter)}xc3x97100. 
In the present invention, the content ratio of matting agents incorporated into the image recording layer side is preferably from 0.2 to 10 percent by weight with respect to the total solids of the image recording layer side, or alternatively the added amount is preferably 40 to 800 mg per
Further, the content ratio of matting agents incorporated into the backing layer side is preferably from 0.1 to 5 percent by weight with respect to the total solids of the backing layer side, or alternatively the added amount is preferably 4 to 200 mg per m2.
In the present invention, said matting agents may be incorporated into any of the constituted layers. However, in order to achieve the objectives of the present invention, on the image recording layer side, layers other than the image recording layer are preferred, and the outermost layer from the support, namely the protective layer, is more preferred. Further, on the backing layer side, addition is preferably carried out on the outermost layer from the support, namely the protective layer.
In the present invention, methods for adding said matting agents include a method in which said matting agents are previously dispersed into a coating composition followed by coating the resultant composition, and a method in which after coating a coating composition, said matting agents are sprayed onto the coating prior to its drying. Further, when a plurality of matting agents is applied, both methods may be used in combination.
In addition to the aforesaid methods, other methods, which may be employed to adjust said glossiness, include, for example, a calender roller treatment applied to the coating surface, coating of a filler containing overcoat layer, coating of foaming resins, minute embossing, mechanical polishing utilizing an abrasive dispersion treatment, and mechanical polishing utilizing a brush. A suitable method may be selected from these and employed, or some of these may be employed in combination.
Contrast increasing agents, represented by Formula (1) or (2), will now be described.
The invention according to items (3) and (5) is characterized in that an image recording layer or its adjacent layer comprises the contrast increasing agents represented by the aforesaid Formula (1).
The contrast increasing agents represented by Formula (1) will now be detailed.
In the aforesaid Formula (1), at least one of R1 and R2 represents a cyano group and the alternate represents an optional univalent substituent. M represents a hydrogen atom or an alkali metal atom.
In Formula (1), cited as univalent groups are, for example, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, a heterocyclic ring group, a quaternary nitrogen atom-containing heterocyclic group (for example, pyridinium group), a hydroxy group, an alkoxy group (for example, including a group which contains repeated units of an ethyleneoxy group or a propyleneoxy group), an aryloxy group, an acyloxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, a carbamoyl group, a urethane group, a carboxyl group, an imido group, an amino group, a carboxamido group, a sulfonamido group, a ureido group, a thioureido group, a sulfamoylamino group, a semicarbazido group, a thiosemicarbazido group, a hydorazino group, a quaternary ammonia group, an alkylthio group, an arylthio group, a heterocyclic thio group, a mercapto group, an alkylsulfonyl group, an arylsulfonyl group, an alkylsulfinyl group, an aryl sulfinyl group, a sulfo group, a sulfamoyl group, an acylsulfamoyl group, an alkylsulfonylureido group, an arylsulfonylureido group, an alkylsulfonylcarbamoyl group, an arylsulfonylcarbamoyl group, a halogen atom, a cyano group, a nitro group, and a phosphoric acid amido group.
Further, listed as alkali metal atoms are sodium and potassium.
The preferred specific examples of contrast increasing agents represented by Formula (1) according to the present invention will now be illustrated. However, the present invention is not limited to these examples. 
The compounds represented by Formula (1) of the present invention, when incorporated into said image recording layer or its adjacent layer, function as contrast increasing agents and are capable of more effectively exhibiting the desired effects of the present invention.
The amount of the compounds added, represented by Formula (1), is preferably in the range of 0.001 to 0.3 mol per mol of silver atom incorporated into the image recording layer, and is more preferably in the range of 0.005 to 0.05 mol.
One of the features of the invention according to items (4) and (6) is that an image recording layer or its adjacent layer comprises the contrast increasing agents represented by the aforesaid Formula (2).
The contrast increasing agents represented by Formula (2) will now be detailed.
In aforesaid Formula (2), M represents a hydrogen atom or an alkali metal atom and L represents a divalent organic group necessary for forming a cyclic ring structure.
L1 in Formula (2) represents an individual group or combination of, for example, an alkylene group (for example, a methylene group, an ethylene group, a 1,2-propylene group, a 1,4-butylene group, and a 1,2-cyclohexylene group), an arylene group (for example, a 1,2-phenylene group, a 1,3-phenylene group, a 1,4-phenylene group, a 1,2-naphthylene group, and a 9,10-anthranylene group), an alkenylene group, xe2x80x94SO2xe2x80x94. xe2x80x94SOxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, and xe2x80x94N(R3)xe2x80x94, wherein R3 represents an alkyl group, an aryl or a hydrogen atom).
Further, cited as alkali metal atoms are sodium and potassium.
The preferred specific examples of contrast increasing agents represented by Formula (2) according to the present invention will be demonstrated below. However, the present invention is not limited to these examples. 
The compounds represented by General Formal (2) of the present invention, when incorporated into said image recording layer or its adjacent layer, function as contrast increasing agents and are capable of more effectively exhibiting the desired effects of the present invention.
The amount of the compounds added, represented by Formula (2), is preferably in the range of 0.001 to 0.3 mol per mol of silver atom incorporated into the image recording layer, and is more preferably in the range of 0.005 to 0.05 mol.
In the present invention, other than the contrast increasing agents represented by aforesaid Formula (1) or (2), other contrast increasing agents, known in the art, may be employed individually or in combination.
Listed as other contrast increasing agents usable in the present invention may be those described in Research Disclosure (hereinafter referred to as RD) 23515 (November 1983, page 346) and references cited therein; and U.S. Pat. Nos. 4,080,207, 4,269,929, 4,276,364, 4,278,748, 4,385,108, 4,459,347, 4,478,928, 4,560,638, 4,686,167, 4,912,016, 4,988,604, 4,994,365, 5,041,355, and 5,104,769; British Patent No. 2,011,391B; European Patent Nos. 217,310, 301,799, and 356,898; Japanese Patent Publication Open to Public Inspection Nos. 60-179734, 61-170733, 61-270744, 62-178246, 62-270948, 63-29751, 63-32538, 63-104047, 63-121838, 63-129337, 63-223744, 63-234244, 63-234245, 63-234246, 63-294552, 63-306438, 64-10233, 1-90439, 1-100530, 1-105941, 1-105943, 1-276128, 1-280747, 1-283548, 1-283549, 1-285940, 2-2541, 2-77057, 2-139538, 2-196234, 2-196235, 2-198440, 2-198441, 2-198442, 2-220042, 2-221953, 2-221954, 2-285342, 2-285343, 2-289843, 2-302750, 2-304550, 3-37642, 3-54549, 3-125134, 3-184039, 3-240036, 3-240037, 3-259240, 3-280038, 3-282536, 4-51143, 4-56842, 4-84134, 2-230233, 4-96053, 4-216544, 5-45761, 5-45762, 5-45763, 5-45764, 5-45765, 6-289524, and 9-160164.
In addition to these compounds, employed may be compounds represented by (Ka 1) described in Japanese Patent Publication No. 6-77138, specifically including compounds on pages 3 and 4; compounds represented by Formula (1) in Japanese Patent Publication No. 6-93082, specifically including compounds 1 through 38 on pages 8 to 18; compounds represented by Formulas (4), (5), and (6) described in Japanese Patent Publication Open to Public Inspection No. 6-23049, including compounds 4-1 through 4-10 described on pages 25 and 26, compounds 5-1 through 5-42 on pages 28 through 36, and compounds 6-1 through 6-7 on pages 39 and 40; compounds represented by Formulas (1) and (2) described in Japanese Patent Publication Open to Public Inspection No. 6-289520, specifically including compounds 1-1) through 1-17) and 2-1) on pages 5 through 7; compounds represented by (Ka 2) and (Ka 3) described in Japanese Patent Publication Open to Public Inspection No. 6-313936, specifically including compounds on pages 6 through 19; compounds represented by (Ka 1) described in Japanese Patent Publication Open to Public Inspection No. 6-313951, specifically including compounds on pages 3 through 5; compounds represented by Formula (I) described in Japanese Patent Publication Open to Public Inspection No. 7-5610, specifically including compound 1-1 through I-38 on pages 5 through 10; compounds represented by Formula (II) described in Japanese Patent Publication Open to Public Inspection No. 7-77783, specifically including compounds II-1 through II-102 on pages 10 through 27; and compounds represented by Formulas (H) and (Ha) described in Japanese Patent Publication Open to Public Inspection No. 7-104426, specifically including compounds H-1 through H-44 on pages 8 through 15.
Each of the components, other than those described above, of the photothermographic materials employed in the present invention, will now be described.
In the photothermographic materials employed in the present invention, the following materials are preferably employed by adding any of those to the constitution of the present invention: silver halides described in paragraphs [0089] through [0101] of Japanese Patent Publication Open to Public Inspection No. 2001-56521; organic silver salts described in paragraphs [0135] and [0136] of Japanese Patent Publication Open to Public Inspection No. 2001-13661: reducing agents described in paragraphs [0125] through [0131] of Japanese Patent Publication Open to Public Inspection No. 2000-310832; binders described in paragraphs [0142] through [0145] of Japanese Patent Publication Open to Public Inspection No. 2000-310832; retarding agents described in paragraphs [0070] through [0088] of Japanese Patent Publication Open to Public Inspection No. 2001-56521; color controlling agents described in paragraphs [0111] through [0113] of Japanese Patent Publication Open to Public Inspection No. 2001-56521: dyes described in paragraph [0116] of Japanese Patent Publication Open to Public Inspection No. 2000-310832; dyes described in paragraph [0116] of Japanese Patent Publication Open to Public Inspection No. 2001-310832; supports, subbing layers, and antistatic layers described in paragraphs [0122] through [0125] of Japanese Patent Publication Open to Public Inspection No. 2001-13660.
Further, various additives may be incorporated into any of the image recording layer, the non-image recording layer, or other layers. Additives such as surface active agents, antioxidants, stabilizers, plasticizers, UV absorbers, and coating aids may be employed in the photothermographic materials of the present invention. Preferably employed as these additives, as well as the aforesaid additives, may be compounds described in RD Item 17029 (June 1978, pages 9 through 15).